Successful abrogation of lung Ischemia/reperfusion (I/R) injury could significantly improve short- and long-term outcomes for lung transplant recipients, as well as potentially expand the use of marginal donor organs. Reactive oxygen species (ROS) generated during I/R are clearly detrimental. A therapeutic approach of selectively scavenging detrimental ROS elements, such as hydroxyl radicals (OH(), but sparing ROS involved in antimicrobial defense and NO signaling, is desirable in order to ameliorate I/R injury and maximize short and long-term outcomes after lung transplantation. Inhaled hydrogen gas (1-4%) selectively reduces detrimental hydroxyl radicals and peroxynitrite, but does not decrease the steady-state levels of NO, superoxide anion or hydrogen peroxide. Hydrogen is highly diffusible and can potentially reach sub-cellular compartments, such as the mitochondria and nuclei, which are the primary sites of ROS generation and DNA damage but are notoriously difficult to target. Furthermore, inhaled hydrogen gas has been safely utilized for treatment of decompression syndrome in divers, suggesting that hydrogen can be safely administered to patients. Although hydrogen is known to be highly flammable, it has no risk of explosion at concentrations less than 4.7%. Preliminary experiments were conducted using a rat orthotopic left lung transplantation model with 6 hrs of cold ischemic time. The recipients received hydrogen treatment (2% hydrogen in 98% oxygen) during surgery and 1 hr after reperfusion and demonstrated significantly improved graft gas exchange early after reperfusion as compared to recipients in the control group (2% nitrogen and 98% oxygen). Hydrogen-treated animals also had less upregulation of proinflammatory cytokine mRNA and less lipid peroxidation 2 hrs after reperfusion. Hypothesis: The proposed research will investigate the hypothesis that inhaled hydrogen gas can reduce short- and long-term graft I/R injuries during lung transplantation. It further seeks to determine an optimal hydrogen dosing regimen in the animal model, in order to develop a clinically applicable strategy utilizing hydrogen gas to ameliorate lung cold I/R injury in humans. We propose to test these hypotheses through the following specific aims: Aim 1 Investigate the effects of inhaled hydrogen therapy on I/R injury in a rat model of lung transplantation. Aim 2. Develop clinically relevant protocols of inhaled hydrogen therapy. Inhaled hydrogen is a safe and easily delivered agent that shows great promise in the amelioration of I/R injury. This proposal seeks to provide a strong fundamental basis for inhaled hydrogen gas therapy in lung transplantation, in a manner that will lead directly to clinical trials. PUBLIC HEALTH RELEVANCE: Reducing or eliminating lung ischemia/reperfusion (I/R) injury could significantly improve short- and long-term outcomes for lung transplant recipients, as well as expand the donor pool by facilitating the use of marginal donor organs. Hydrogen gas alleviates oxidative injury (such as that seen during I/R) by selectively neutralizing hydroxyl radicals but hydrogen gas therapy has not been tested in the transplant setting. The objective of this study is to develop a clinically applicable, effective, and safe strategy for the delivery of hydrogen gas to facilitate lung transplantation.